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1.
Transmission fluctuation spectrometry with spatial correlation (TFS‐SC) is based on transmitting two beams of radiation through a flowing suspension, whereby the distance of the beam centers is varied. Thus, the spatial correlation of the transmission fluctuations of the two beams is determined as a function of the beam distance. By numerical modeling, the transition functions of the correlation are found as a function of beam distance, beam diameters, particle diameter and beam intersection angle. Experimentally determined spatial correlation spectra can be inverted to obtain the particle concentration and particle size distribution by using the theoretical transition functions for mono‐sized particles. In addition, time correlations can be used to extract information on particle velocity. Some experimental results obtained by TFS‐SC are presented and discussed. This method appears promising for application in the local resolving of measurements of PSD, particle concentration and particle velocity in two‐phase flows, both in the laboratory and in process control. 相似文献
2.
从超短脉冲光束的傍轴传输方程出发,得出了描述任意脉冲形式驱动的等衍射超短脉冲厄米高斯光束在自由空间中的解析表达式. 并通过例子研究了超短脉冲厄米高斯光束的传输性质. 结果表明:在传输过程中,由于群速度的空间分布不均匀性,会导致超短脉冲光束的脉冲时间延迟,并进而导致了在脉冲不同位置处光束横向分布严重偏离了厄米高斯函数. 另外,在传输过程中,发现不同阶数的脉冲厄米高斯光束会发生不同次数的极化反转. 并用脉冲光束的群-相速度差对这一现象进行了解释.
关键词:
超短脉冲
厄米高斯光束 相似文献
3.
A. N. Kuftin V. K. Lygin V. N. Manuilov A. S. Postnikova V. E. Zapevalov 《International Journal of Infrared and Millimeter Waves》1999,20(3):361-382
The paper presents a modern approach to studies of characteristics of intense helical electron beams (HEBs) for gyrotrons. The essence of the method consists in finding functions of electron distribution with respect to oscillatory velocities in the beam both by numerical simulation and experimentally. Experimental and calculated data for beams with different topologies were compared in different frequency ranges. Evolution of the electron oscillatory velocities distribution function as the beam current grows has been traced. Influence of the reflected electrons on beam parameters has been simulated numerically. 相似文献
4.
The effect of the electron transverse and longitudinal velocity spread at the entrance to the interaction space on wide-band chaotic oscillations in intense multiple-velocity beams is studied theoretically and numerically under the conditions of formation of a virtual cathode. It is found that an increase in the electron velocity spread causes chaotization of virtual cathode oscillations. An insight into physical processes taking place in a virtual-cathode multiple-velocity beam is gained by numerical simulation. The chaotization of the oscillations is shown to be associated with additional electron structures, which were separated out by constructing charged particle distribution functions. 相似文献
5.
Jensen JA 《Ultrasonics》2000,38(1-8):358-362
Ultrasound has been used intensively for the last 15 years for studying the hemodynamics of the human body. Systems for determining both the velocity distribution at one point of interest (spectral systems) and for displaying a map of velocity in real time have been constructed. A number of schemes have been developed for performing the estimation, and the various approaches are described. The current systems only display the velocity along the ultrasound beam direction and a velocity transverse to the beam is not detected. This is a major problem in these systems, since most blood vessels are parallel to the skin surface. Angling the transducer will often disturb the flow, and new techniques for finding transverse velocities are needed. The various approaches for determining transverse velocities will be explained. This includes techniques using two-dimensional correlation (speckle tracking), multiple beams, and the new transverse modulation technique. The different advantages and disadvantages of the approaches are explained. 相似文献
6.
根据8 mm回旋速调管放大器对双阳极磁控注入电子枪的要求,分析了电极形状、阳极电压、磁场、注电流对电子注横纵速度比和速度零散的影响,并进行了粒子模拟。分析表明:这些因素可归根为电场和磁场的作用,阴极附近高的电场有助于提高横纵速度比和降低速度零散;而高的磁场及低的磁压缩比将降低横纵速度比,但对速度零散影响无明显规律。在此基础上通过优化电极形状、磁场分布、电流、第一阳极电压和第二阳极电压,模拟并试制出工作电压65 kV、电流12 A、磁场1.4 T的双阳极电子枪,得到的横纵速度比值为1.4,横向速度零散为4.5%, 为8 mm回旋速调管提供了稳定高质量的电子注。 相似文献
7.
This paper describes a technique aimed at measuring particle size by light scattering from gaussian laser beams. The uncertainties in illumination due to the beam shape are avoided by determination of the direction and velocity. The method, which we arbitrarily called the Two Beam System (TBS), uses a simple birefringent prism to separate the incident laser beam into two orthogonally polarised overlapping parallel beams. The relative delay and amplitudes of the intensities scattered out of the orthogonal polarisations are indicative of the particle direction and velocity. Having obtained the direction of travel of the particle, its size is then obtained from the scattered intensity using Mie theory. 相似文献
8.
A. I. Artem’ev D. N. Klochkov K. Oganesyan Yu. V. Rostovtsev M. V. Fedorov 《Laser Physics》2007,17(10):1213-1216
The spatial amplification of a wave in a magnetostatic undulator with noncollinear electron and laser beams is studied in the framework of the dispersion relation for single-frequency and collective regimes. The dependence of the gain on the electron beam width is estimated with regard to the spatial boundedness of the beams. The laser power threshold at which the selection with respect to the transverse velocity is possible is obtained for a free-electron laser without inversion. 相似文献
9.
10.
N. N. Rozanov 《Optics and Spectroscopy》2006,100(2):257-260
It is shown that the velocity of the centers of inertia of localized structures of an electromagnetic field in vacuum does not exceed the speed of light in vacuum. The relation of this constraint with the properties of so-called X waves is discussed. For linear homogeneous anisotropic (dichroic) media, the transverse motion of the centers of Gaussian beams of monochromatic radiation is analyzed. It is found that, in the general case, the beam center moves along a hyperbola (curvilinearly), and, if the field envelope distribution is axisymmetric, this motion is rectilinear. 相似文献
11.
基于绝热压缩原理和强流电子光学理论,设计了一只170 GHz回旋管双阳极磁控注入电子枪,经过理论分析及计算,采用仿真软件进行模拟和优化,最终得到的电子枪的电子注速度比为1.31,横向速度零散度为3.5%,纵向速度零散度为6.1%,束电流为51 A。讨论了阴极磁场、控制阳极电压和第二阳极电压等因素对电子注性能的影响,发现电子注的速度比和速度零散度对这些影响因子的变化都非常敏感:随着阴极磁场的增大,电子注的速度比减小,纵向速度零散度先增大后减小,横向速度零散度先减小后增大;阳极角越接近阴极倾角,纵向速度零散度越小;阳极角向着减小阴阳极间距的方向变化时横向速度零散度变小;增大第一阳极电压可以增大电子注的速度比和电子注的速度零散度。在两阳极电压不变的情况下,增大阴阳极之间的距离会使电子注的速度零散度和电子注的速度比减小。 相似文献
12.
V.G. Minogin 《Optics Communications》1980,34(2):265-268
Deceleration and velocity distribution narrowing of an atomic beam irradiated by a counter-running resonant light wave is discussed. Velocity distribution evolution under the action of light pressure force and diffusion is found. The results of a numerical solution of the kinetic equation for the atomic velocity distribution function are presented. These results show the efficiency of using the light pressure to decelerate atomic beams and narrow their velocity distribution. 相似文献
13.
We present three-dimensional, fully relativistic, fluid simulations of the dynamics of inhomogeneous counter streaming beams with the aim of understanding the magnetic structures that can be expected to form as a consequence of the development of the so-called Weibel instability. Ringlike structures in the transverse direction are generated as a consequence of the development of a spatially resonant mode. We describe the structures generated by beams of equal initial density and velocity and by a fast, less dense beam compensated by a slower, denser beam. We consider these two cases as schematic models of a laser produced beam propagating in a plasma with nearly equal density and in a plasma much denser than the injected beam. 相似文献
14.
The approximate analytical expressions of the apertured broadband beams in the far field with Gaussian and Laguerre-Gaussian spatial modes are presented.For the radially polarized Laguerre-Gaussian beam,the result reveals that the electromagnetic field in the far field is transverse magnetic.The influences of bandwidth(Γ) and truncation parameter(C 0) on the transverse intensity distribution of the Gaussian beam and on the energy flux distribution of radially polarized Laguerre-Gaussian beam are analysed. 相似文献
15.
Polarization transverse distribution of multi-Gaussian Schell photon beams in a turbulent atmosphere
The analytical expression for the polarization transverse distribution of multi-Gaussian Schell photon beams propagating through the modified von Karman turbulence channel are studied, in consideration with the effects of outer and inner scale of turbulence. It is found that the zenith angle has a very slight effect on the degree of polarization of photon beams. In the area near to the beam center, the degree of polarization increases as the source's transverse size and source's transverse coherent width increases, or sub-beam number M decrease. However, in the area away from the beam center, increasing value of sub-beam number M or decreasing the source's transverse coherent width and the source's transverse size, larger the degree of polarization of beams is achieved. 相似文献
16.
A formula is developed to describe the propagation of beams driven by few-cycle Gaussian pulse in a media with group velocity dispersion (GVD). With the method, the spatiotemporal evolution of the pulsed beam can be straightforwardly quantified as long as the monochromatic beam solutions in free space, which have been widely investigated in previous works, are known. The method makes it possible to analytically deal with the few-cycle pulsed beams with transverse profiles other than the Gaussian one, which is, to our knowledge, the one mainly investigated previously, in GVD media. 相似文献
17.
The transformations of the transverse profiles of laser beams in a nonlinear Fabry-Perot interferometer based on lithium niobate
crystals with a surface layer doped with a combination of photorefractive impurities (iron and copper ions) have been experimentally
investigated. It is demonstrated that the distribution of transmitted beam intensity significantly changes for a few seconds
at milliwatt beam powers. 相似文献
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19.
A beam is described by its transverse power density distribution, its wavefront, and its transverse distribution of coherence. The beam propagation ratio, M2, is expressed as the square root of the sum of each of the three beam attributes. The shape of the power density distribution governs the diffraction of the beam. The stronger it is modulated, the higher the M2. In comparison to an non-aberrated beam, the M2 of a beam with an aberrated wavefront is increased. Similarly, the M2 of a partially coherent beam is higher than the one of a fully coherent one. A concise formula is derived. The components of M2 of a mixture of Hermite–Gaussian beams and of a spherically aberrated Gaussian beam are given as examples. 相似文献